Conventional copper foils having been used for manufacturing of printed wiring boards, as disclosed in many documents including Patent Document 1, are subjected to a roughening treatment to make one surface uneven by adhering fine copper particles or by other means. When it is laminated with a base resin such as a prepreg, the unevenness shape of roughened surface of the copper foil buried in the base resin works as anchor effect, whereby the good adhesion of the copper foil and the base resin is assured.
In the case of an electrodeposited copper foil as example, a bulk copper layer as a base body of an electrodeposited copper foil is obtained from procedures, a copper electrolyte solution supplied into the gap between a drum-shaped rotating cathode and a lead-based anode or the like which is facing with and disposed along the shape of the rotating cathode, deposited copper as a foil state on the drum surface of the rotating cathode by utilizing electrolytic reaction, and then continuously peel off the copper foil from the rotating cathode.
The one surface of the electrodeposited copper foil thus obtained is referred to as a shiny surface. Because the surface has been in contact with a rotating cathode so it has mirror shape of the mirror-finished rotating cathode surface, and is a glossy smooth surface. On the other hand, the surface shape on the solution side which has been a deposition side assumes an angular unevenness shape because crystal growth rates of copper deposition are different for every crystalline plane, so the surface is referred to as a matte surface. This matte surface is ordinarily used for a laminating surface with an insulation material when a copper-clad laminate is manufactured.
Then, this non-treated foil is subjected to a roughening treatment and a rustproof treatment on the matte surface in a surface treatment process. The roughening treatment on the matte surface means that a current condition of the so-called burning plating condition is applied in a copper sulfate solution, depositing fine copper particles on the angular unevenness shape of the matte surface, and immediately being subjected to a seal plating in a current condition for the level plating, and is to prevent dropping-off of the fine copper particles. Therefore, the matte surface on which fine copper particles have been deposited and adhered is referred to as “roughened surface”. Then, an electrodeposited copper foil is finished by being subjected to a rustproof treatment, etc if required.
However, in recent years, with the tendency of light-weight and miniaturization of electronic devices for which printed wiring boards are applied, the demand for the wiring density of printed wiring boards has increased year by year. Moreover, the improvement in product quality has been requested; the precision on circuit shapes formed by etching has also been highly requested; and for etching factor of the circuit, a level where the impedance control can be completely performed has been requested.
Then, for solving such a problem in the circuit etching factor, as disclosed in Patent Document 2, an attempt to obtain a favorable adhesion after lamination, etc. even without the roughening treatment, for assurance of the adhesion with a base resin, two resin layers having different compositions are formed on the surface of a copper foil without roughening treatment. Moreover, to get the circuit shape after etching in a good shape, thinner copper foil layer to be etched has been desired. For responding to this requirement, as disclosed in Patent Document 3, the electrodeposited copper foil with carrier foil is supplied to the markets for a long time. Since in the electrodeposited copper foil with carrier foil, the carrier foil works as a supporter in the state of being bonded with the electrodeposited copper foil layer, it has advantages of thinning of the copper foil layer with ease, handling thereof with ease, no occurrence of wrinkles and no contamination of the copper foil surface.
Patent Document 1: Japanese Patent Laid-Open No. 05-029740
Patent Document 2: Japanese Patent Laid-Open No. 11-10794
Patent Document 3: Japanese Patent Laid-Open No. 2000-43188
However, as far as the present inventors know, it is found that even if a resin-coated copper foil disclosed in Patent Document 2 is used, the copper foil surface without roughening treatment does not provide a stable adhesion with a base resin. Additionally, since it is provided with two resin layers having different compositions, two or more coating processes are required for manufacturing of the resin layers, thus it increases the manufacturing cost.
On the other hand, if a copper foil without roughening treatment can be used for manufacture of a printed wiring board, the above-mentioned roughening treatment process of a copper foil can be eliminated. Consequently, it makes a large reduction of the production cost possible, and it also leads to surviving in the recent years' international cost competition in fact. Moreover, there is no roughening treatment of the copper foil, an over etching time for dissolving roughening-treated parts in circuit etching is not required to enable reduction of the total etching cost, so the etching factor of the obtained circuit may remarkably improved.
As shown above, it is clear that use of a copper foil without roughening treatment for a printed wiring board has been thought as an un-applicable technology in industry. But, if a copper foil without roughening treatment can be used for manufacture of a printed wiring board, the total manufacturing cost of the printed wiring board can be remarkably reduced. Further, if this problem can be solved with the electrodeposited copper foil, thinner the copper foil can be evident and it gives a great effect on markets.